1. Field of the Invention
This invention relates to a wiper blade rubber which offers inconspicuous sliding resistance and excels in resistance to weather conditions and resistance to ozone cracking.
2. Description of the Prior Art
Referring to FIG. 6 generally wiper blade rubber stock is molded in the form of a strip the cross section of which comprises in combination a base part 1 of large thickness, a roughly triangular vibration part 3 connected through the medium of a neck part 2 to the aforementioned base part 1, and a lip part 4 of the shape of a thin plate formed at the leading end of the aforementioned vibration part 3, as illustrated in FIG. 6. The stock, as formed into wiper blade rubbers, is used as a wiping member of a wiper and adapted to slide on the outer surface of a windshield such as that of an automobile and serves to remove water drops adhering on the outer surface by the sliding motion of the wiping member on the windshield.
The usual wiper blade is formed of natural rubber or a blend of natural rubber with chloroprene rubber or a diene rubber such as styrene-butadiene rubber or butadiene rubber. Thus, it has the merit of possessing flexibility and, at the same time, the demerit of offering high sliding resistance. When the conventional wiper blade uses a diene rubber, the double bond in the rubber composition used to make the wiper blade is oxidized by the ozone in the air and consequently is caused to sustain ozone cracking. The conventional wiper blade, therefore, has detrimental feature particularly that the neck part 2 exhibits sufficient durability.
As means of lowering the sliding resistance of the wiper blade rubber, the method of hardening the wiper blade rubber by chlorinating the surface and the method of covering the wiper blade rubber with a surface layer containing a finely divided sliding powder such as powdered molybdenum disulfide have been known to the art. The chlorinated surface of diene rubber is less liable to ozone cracking. When the surface of the wiper blade rubber is wholly chlorinated, it is so rigid that it will not conform to the contour of the surface of the windshield with sufficient smoothness. It is, therefore, necessary that the treatment of chlorination should be performed mildly as a whole or should be given to the wiper blade rubber except for the neck part 2. So long as any diene rubber is used in the wiper blade rubber, the occurrence of ozone cracking cannot be precluded. The aforementioned surface layer containing the finely divided sliding powder such as powdered molybdenum is useless in preventing the occurrence of ozone cracking.